Covers of the above-described kind are previously known in a variety of configurations. Examples of such configurations are found in SE-B 452 287. In FIG. 4 in said document it is shown that each of the two portions between the creasing lines 5 and 7 and 6 and 8, respectively, make an obtuse angle with the spine 3 such as to form a gap between said portions and the strip of binding agent 4. If a sheaf of papers is inserted between the substantially parallel cover sides into contact with the strip, the outermost sheets of papers in the sheaf will fall down into the gaps between the strip and the two portions, wherefore the outermost sheets of paper in the sheaf will not contact the strip and will therefore not be connected to the cover on subsequent activation of the strip.
In order to eliminate this disadvantage, the longitudinal side edges of the strip may be connected to said portions before the sheaf of papers is inserted in the cover. This is shown in FIGS. 1 and 2 in the above-mentioned patent specification.
Said measure brings a solution to the problem encountered and implies an increase in the quality of the cover and therefore of the finished booklet, however, also increased costs of manufacturing the cover.